Re: [PATCH V13 03/10] mmc: block: Add blk-mq support

From: Linus Walleij
Date: Fri Nov 10 2017 - 05:19:22 EST


Following up on this:

On Thu, Nov 9, 2017 at 4:52 PM, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:

>> No one has ever suggested that the legacy API will remain. Once blk-mq is
>> ready the old code gets deleted.
>
> The block layer maintainers most definately think MQ is ready
> but you seem to disagree. Why?
>
> In the recent LWN article from kernel recepies:
> https://lwn.net/Articles/735275/
> the only obstacle I can see is a mention that SCSI was not
> switched over by default because of some problems with
> slow rotating media. "This change had to be backed out
> because of some performance and scalability issues that
> arose for rotating storage."
>
> Christoph mentions that he's gonna try again for v4.14.
> But it's true, I do not see that happening in linux-next yet.

Neil Brown's article on LWN points to Ming Lei's patch
set:
https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1513023.html

As addressing the issue that held back blk-MQ from
being default for SCSI, and it is reportedly to be
queued for v4.15. Since this MMC/SD rework is
also targeted for v4.15 I think we can assume it is
pretty much ready for everything, and delete the
non-MQ block path.

I just haven't seen any of this problem in my tests
with MMC/SD so I do not think it would be affected,
but it anyways seem to be fixed.

OK maybe I am especially optimistic. But it's not just
based on that.

Yours,
Linus Walleij